6 - Connective Tissues & Friends

Not Inflammation ?

A crucial step in the defenses recruited by the mast cell is not included in the cardinal features of inflammation. Recall that mast cells secrete neutrophil and eosinophil chemotactic factors. These cytokines cause these two white cell types to leave the blood vessel in the area of inflammation, and migrate towards the area of infection. Once there, the neutrophils can help destroy the invaders and the eosinophils then act to keep the responses of the defensive cells under control. In particular, the eosinophils turn off the attack, once the invaders have been routed.

****CLASSIFY AND IDENTIFY

Classify the Tissue: Dense Irregular Connective Tissue Identify the layer: Dermis

****CLASSIFY AND IDENTIFY

Classify the Tissue: Unilocular Adipose Tissue Identify the layer: Hypodermis

Connective Tissue Classes

Connective Tissue is one of the 4 basic tissue types, along with epithelial, muscle and nervous tissues. It is characterized by the predominance of extracellular matrix, compared to the presence of cells. This property is not present in the other tissue classes, which are dominated by cells. The primary function of connective tissue proper is an important one- it literally holds our bodies and organs together. It also protects the structures it encloses from attacks: both physical and by microorganisms.

reticular fibers

Fibers made of collagen fibers that are very thin and branched. Forma tightly woven fabric that joins connective tissue to adjacent tissues. Reticular fibers are made by a specialized type of fibroblast called a reticulocytes.

Fibroblasts & Myofibroblasts

Fibroblast are important for collagen turnover myofibroblast are important for movement

Fixed Cells

Fibroblasts/ Fibrocytes Adipose Cells Mast Cells Macrophages Pericytes

What occurs during inflammation

Histamine and leukotrienes produced by the activated mast cell causes local vascular dilation. The vascular dilation provides for increased blood flow, which is in turn responsible for the redness (rubor) and heat (calor).

inflammation/swelling

Histamine, leukotrienes and bradykinin also affect the tight junctions between capillary endothelial cells, causing the endothelial lining to become leaky and allowing plasma proteins to leak out of the vessels. This upsets the normal movement of water, increasing the amount of water pulled into the extracellular space. The result is swelling (tumor). This leakiness also makes it easier for white blood cells to exit the bloodstream and join the fight against the invading micro-organism. Bradykinin also directly activates pain receptors leading to pain and tenderness in the affected region (dolor).

dense connective tissues

In contrast to areolar connective tissue, dense irregular connective tissue is characterized by the predominance of numerous bundles of apparently randomly oriented collagen fibers. The cells are few and far between. The collagen fibers are made and organized by fibroblasts. ******Common places to find this type of tissue are: the dermis of the skin, the capsules of organs, and in the submucosa of the GI tract (shown here).

Macrophages in Response to Infections

In response to phagocytosing micro-organisms, the macrophage becomes activated and releases TNFα and Il-1. This induces endothelial cells to express selectins and ICAMs on their plasma membranes.

Myofibroblasts

In wound healing, more extensive collagen synthesis must take place. At first, synthesis is the major task, but then the fibroblasts need to actually move collagen fibers about to remodel the area of scar tissue. To do this they start expressing myosins, and are rechristened myofibroblasts. This process results in a gradual diminishing of scars. Note that in some individuals, particularly among those of African descent, this process does not take place, and they are prone to over-production of collagen, producing keloids. This trait makes plastic very surgery inadvisable.

Collagenopathies Or Why Pirates had Bad Teeth

Individuals with problems in pathways for producing collagen can present with a number of different diseases. Two you should be aware of: Scurvy (Hypovitaminosis C) Ehlers-Danlos Syndrome

******Major Collagen Types

know 1-5 and 7 ****MAKE SURE YOU KNOW THE CHART (MAKE SLIDES)

Metachromasia:

literally, changing color. Mast cells exhibit this property. With this toluidine stain, they change the light blue stain color into a purplish tone.

Transient cells

Adipose Cells Mast Cells Macrophages Pericytes Transient Cells Plasma cells Lymphocytes Neutrophils Eosinophils Macrophages

Macrophages in Response to Infection - step 4

4. The white blood cells then move to the infection site using chemotaxis, in response to the concentration gradient of IL-8 secreted by the macrophage.

Macrophages in Response to Infection - step 3

3. At this point the white blood cell moves between the endothelial cells to exit the vessel and enter the tissue. This process of passing through the endothelium is referred to as diapedesis or extravasation.

Main Types of Glycosaminoglycans

*** look at the pic Note that all these GAGs are all sulfated except hyaluronic acid. All of them undergo their final synthesis in the Golgi apparatus, except hyaluronic acid. It is synthesized on the cytoplasmic surface of the plasma membrane and then exported into the extracellular fluid by integral membrane proteins forming a channel. Hyaluronic acid is also much bigger than the sulfated GAGs. Its molecular mass is 107-109 daltons, while the sulfate GAGs range between 1-3 X 103 daltons.

Mast cell products

****know these pic

Connective tissues classes

1. Connective Tissue Proper 2. Embryonic Connective Tissue 2. Skeletal Tissues (Bone & Cartilage) 3. Blood ignore -- We will discuss Skeletal Tissues and Blood in separate lectures, as they are more specialized than connective tissue proper, and represent more complicated topics.

Macrophages in Response to Infection - step 1

1. Selectins interact weakly with cell surface molecules on white blood cells (neutrophils, monocytes and eosinophils) causing them to roll along the surface of the vessel and slow down.

ECM fluid functions

1. Support - sustenance and oxygen provided by the ECM fluid; materials dissolves in the ECM fluid and enters the flood stream (oxygen can enter the lungs) 2. Excretion - ECM can be used as sewer system; many are removed by the kidney to leave as urine, CO2 exits by the lungs. 3. Communication - Chemical messengers in the ECM fluid are used for communication from neighborhood; cells in distant location, the messenger travels in the ECM fluid to reach the cell (that is how cells in different part of the body is coordinated.

*****KNOW THIS PROCESS -- Collagen Production

1.Like all proteins, collagen production starts by transcription of mRNA from DNA. 2.The preprocollagen molecule is translated from the mRNA and inserted into the rER cistern. 3.It is hydroxylated in the rER. This requires Vitamin C. 4.It is glycosylated in the rER 5.The resultant procollagen molecules assemble into a triple helix in the rER. 6.The Golgi apparatus packages the procollagen complex and secretes it constituitively. 7.Once extracellular, the end peptides which made the molecule soluble, are cleaved by procollagen peptidase, to form insoluable tropocollagen. 8.The tropocolagen spontaneously assembles into collagen fibrils, the tropocollagen units are stabilized by covalent cross links through the action of lysyl oxidase . 1. preprocollagen 2. procollagen 3. tropocollagen 4. collagen Note: preprocollagen hydroxylated in rER glycosylated in rER procollagen secreted via golgi cleaved to tropocollagen self assembly to collagen

Macrophages in Response to Infection - step 2

2. The rolling cells eventually move slow enough that ICAMs can interact with integrins in the white cell membrane. This forms a strong bond that then holds the cells in place. Histologically this is referred to as margination.

mast cell and cAMP

Activation multiple IgE receptors stimulates a pathway in which adenylate cyclase makes cyclic adenosine monophosphate (cAMP) from adenosine triphosphate (ATP). The cAMP stimulates an influx of calcium ions (Ca+2) to produce exocytosis. Mast cells are chalk-full of vesicles, so this is a massive event where not only do vesicles fuse with the plasma membrane, they fuse with each other. They release histamine, heparin and a variety of proteoglycans that can act as chemotactic factors for other immune system cells.

Adipose Connective Tissue

Adipose connective tissue is dominated by the presence of a specialized cell type, the adipocyte. Adipocytes store lipids for the body to use as a metabolic fuel. They are consequently characterized by the presence of lipid inclusions in their cytoplasm. There are two subclasses of adipose tissue: White (Unilocular) Adipose Tissue and Brown (Multilocular) Adipose Tissue.

Dense Regular Connective Tissue

As a dense connective tissue, dense regular connective tissue is still dominated by fibers and has relatively few cells present. However, the collagen fiber are all oriented in the same plane and this forces the cells to also be spaced fairly regularly through the tissue. Note that the collagen fibers are barely stained in the tendon example

Eosinophil features

At the LM level, eosinophils are characterized by a dark, bilobed nucleus and numerous small eosinophilic granules. So how will you tell them from mast cells and other cells with red granules? Answer: the bilobed nucleus. Eosinophils release agents that inactivate the pro-inflammatory products of mast cells, bringing the response to an end. In addition, they phagocytose antigen-antibody complexes, so that they will no longer stimulate immune responses.

macrophages in the light level

At the light microscopic level macrophages are characterized by a large, lightly stained oval nucleus. This does not set them apart much from many other cells. So we use the "You are what you eat" rule. We will only identify well-fed macrophages in the lab. In some cases it is easy to see their phagocytosed contents. These lung cells are filled with dark particles. In other cases it is more challenging to see their phagocytosed contents. These cells in the gut contain pieces of other cells.

Collagen fibers features

Banded appearance The tropocollagen subunits are arranged end to end, but when they are stacked to form a fibril, they are offset. This offset creates gap and overlap regions which line up across the fibril to produce banding. The fibrils are assembled into collagen fibers, and in some cases the fibers are further grouped into bundles.

Scurvy (Hypovitaminosis C)

Because Vitamin C plays a significant role in the hydroxylation of the procollagen molecule, a diet that lacks fresh fruit, meat and vegetables, the main sources of this vitamin, leads to defective collagen formation. Since one of the areas with particularly high collagen turnover is the periodontal ligament, individuals with scurvy tend to lose their loose teeth. They also have weakened vessels and their gums bleed easily. It is estimated that 50% of the sailors in the British Navy suffered from scurvy in the 1800s.

Dense Irregular Connective Tissue (CT) appearance

Depending on the tissue and how it was prepared, dense irregular CT can vary in its appearance, but it is always dominated by random fibers, and has relatively few cells. Note all the space in the submucosa example- this does not make it "loose".

****IDENTIFY THE STRUCTURE OR FIBER INDICATED BY THE POINTER

ELASTIC FIBERS

Identify the structure or fiber indicated by the pointer

ELASTIC LAMINA In blood vessels, we find a specialize organization of elastin, called: elastic lamina. ***to be complete and receive full credit, your answer should indicate this.

Eosinophil

Eosinophils originate from precursor cells in the bone marrow. They have a life span of only 2 weeks, so they are not around for long. However, they are present in large numbers beneath wet epithelia, like the gut mucosa. They have two main functions: 1.They fight parasitic worms 2.They tamp down the inflammatory response produced by mast cells. At EM level, their granules are characterized by a bar called an internum. They contain major basic protein, eosinophilic cationic protein and eosinophilic neurotoxin, all of which kill parasitic worms. ***nucleus has two lobes

Elastic fibers

Flexible and "stretchy" fibers that add elasticity to tissue Elastic fibers are mostly made by fibroblasts, but smooth muscle cells located in blood vessels can also make elastic fibers.

Ground Substances

Ground substance is an amorphous gel-like material made up of 1. glycosaminoglycans 2. proteoglycans 3. glycoproteins Glycosaminoglycans (GAGs): these are very long molecules made up of repeating disaccharide units. One of the repeating disaccharide units is always an amino sugar; hence the name glycosaminoglycan. These molecules have a lot of negative charges associated with the disaccharides and the sulfate groups that are often attached to them. The negative charges attract positively charged sodium ions (Na+). The presence of the sodium ions attracts water into the extracellular space. The negative charges also cause the GAGs to repel each other, making the extracellular fluid feel slippery.

Unilocular Adipocyte Function

Lipids are not generally water soluble. Those absorbed in the intestines must travel in the bloodstream as chylomicrons and in association with very low density lipid particles (VLDL). In the area of adipose tissue, which is generally well vascularized, the capillary endothelial cells break these substances down into free fatty acids using lipoprotein lipase. These can then be reconstituted into triglycerides by the adipocyte and stored in its inclusion. In response to epinephrine from the adrenal glands and autonomic system input, adipocytes use a hormone sensitive lipase to break down the triglycerides in the inclusion into fatty acids, which can then be transported through the bloodstream to sites where they are needed to make energy (ATP).

Lymphocytes

Lymphocytes are responsible for specific immune responses. They are designated a T-cells and B-cells depending on whether they come from the thymus or the bone marrow, respectively. However, this difference can only be determined using immunohistochemical methods. For the purposes of the lab, we will just be identifying lymphocytes. They are able to manufacture antibodies that recognize specific molecules. Normally, these antibodies only recognize non-self. However, if the system fails and you manufacture antibodies to self, then you develop an autoimmune disease. Circulating lymphocytes that have not been activated by meeting an antigen are basically resting cells. They have a dark, spherical nucleus and only a small amount of cytoplasm with relatively few organelles present.

Healing

Macrophages also play a role in healing. Once they have phagocytosed the enemy, the neutrophils undergo apoptosis (programed cell death). The dying neutrophils attract macrophages which then ingest them. These macrophages are then reprogrammed into anti-inflammatory macrophages. They stop secreting TNFα, IL-1 and IL-8. Instead, they secrete IL-10. This interleukin change causes the endothelium to return to normal so that white blood cells are no longer recruited. In addition, the anti-inflammatory phenotype of the macrophage secretes transforming growth factor beta (TGFβ) and fibroblast growth factor (FGF). These cytokines stimulate fibroblasts to repair the damage done by the infection and the actions taken to fight the infection.

Macrophages in Response to Infection

Macrophages are multifunctional cells. They: •Phagocytose invading organisms •Phagocytose senescent cells •Clean up after neutrophils •Present antigens to lymphocytes •Release cytokines to facilitate immune responses and inflammation The cytokines released by macrophages include: Tumor Necrosis Factor alpha (TNFα) and Interleukin 1 (IL-1). These cause the endothelial cells to express: Selectins and Intracellular Adhesion Molecules (ICAMs).

macrophage

Macrophages originate from precursor cells in the bone marrow. These cells develop into monocytes, which circulate in the blood. Eventually they receive a signal that causes them to leave the bloodstream and enter the connective tissue, where they will live for the rest of their lives (~ 2 months). At this point they change their morphology, becoming macrophages. They phagocytose both invading microrganisms and senescent cells in our bodies. Macrophages have numerous cell appendages (pseudopods) and they move through the connective tissue in the fashion of an ameoba. They have the most active phagocytic capabilities of any cell in the body. Consequently their cytoplasm is well stocked with lysosomes and phagosomes (yellow arrows). Their large oval nuclei are often indented.

Multilocular Adipocytes

Makes up the brown fat and though to only be found in infant (baby fat) to deal with cold temperatures by generating heat from fat metabolism. We now know that adults maintain some brown fat. The largest deposit is beneath the clavicle, but there are smaller deposits located in the vicinity of internal organs. The amount of brown fat one has may help determine one's potential for obesity. Multilocular adipocytes have multiple lipid inclusions, are eosinophilic due to their high mitochondrial content, and have nuclei that are not pushed to the edge of the cell.

Mast cell functions

Mast cells are an important part of our immune defense system, but when they malfunction thay can produce allergies or asthma. Their plasma membranes are studded with immunoglobulin E (IgE) receptors. IgE antibodies produced by plasma cells, attach to these receptors giving mast cells the ability to recognize specific antigens. In order to activate the cell, at least two of these IgE molecules have to attach to the same antigen (red arrow), providing a safety factor for mast cell activation.

Mast Cells

Mast cells are derived from bone marrow cell precursors, but spend most of their lives (a few months) in the connective tissue. They are easiest to find in dense irregular connective tissue located beneath the mucosa of the gastrointestinal (GI) tract and in the dermis of the skin. In well stained H&E sections, they will display numerous eosinophilic granules and an oval nucleus that is centrally placed in the cell.

Embryonic Connective Tissue - Mesenchyme

Mesenchyme is made up of undifferentiated cells of mesodermal origin. These cells can develop into a variety of different tissues, e.g., muscle and skeletal. Mesenchymal CT is dominated by cells. You will be hard pressed to find any fibers in the ground substance. That does not mean there is no collagen present, its just rare. Unlike areolar CT, there is only one cell type present: mesenchymal cells. At high magnification you may be able to see little processes connecting these cells.

Embryonic Connective Tissue - Mucous

Mucous connective tissue (also known as Wharton's jelly) is mainly found in the umbilical cord. It displays an extracellular matrix that is dominated by ground substance. It does contain some type I and III collagen fibers, but the large amount of hyaluronic acid gives in a jelly-like feel when examined grossly. At the histological level the extracellular matrix has a smudged appearance, the source of the designation "mucous". Note that the fibroblasts present in this tissue have a dark, flattened appearance, in contradistinction to the lighter spherical nuclei in mesenchyme cells.

Neutrophils

Neutrophils are the infantry of the immune system. They attack invading micro-organisms and kill them in a variety of ways, including phagocytosis. However, they only become activated when they encounter bacteria that have been tagged by antibodies. Neutrophils are manufactured in the bone marrow and access the area where they are needed by way of the blood stream. They only live for a week, but are by far the most numerous of the white blood cells in the blood. However, they only leave the blood when called, so you will see just a few in healthy tissue. After neutralizing the enemy they die and collect as pus. Their their dark nuclei are characterized by the presence of at least three lobes. Their cytoplasm may contain scattered visible granules. Look for them in the duodenal submucosa of SLIDE 248.

Major Collagen Types

Not all collagens form fibers. Some form sheets and some are used as anchors. This figure shows the other morphologies that are present. *****For now, just know Types I-V and VII.

Areolar Connective Tissue

Off the adult connective tissue classes, areolar connective tissue has the most abundant cells and the fewest visible fibers in H&E sections. Found beneath the wet epithelia, but is present in association with other tissues also called loose connective tissue, but this term can lead you astray, as other classes of connective tissue can have a loose arrangement of fibers.

Ground Substance: Proteoglycans

Proteoglycans are formed when sulfated GAGs are attached to a protein core. Many of these have what is called a bottlebrush configuration. They are often quite large (upwards of 50,000 daltons). ****Functions: 1.Occupy large volumes 2.Resist movement of microorganisms & cancer cells 3.Form molecular filters in the basal lamina 4.Have binding sites for signaling molecules 5.Some are transmembrane proteins that control interactions between the cell and matrix

Ground Substance: Proteoglycan aggregates

Proteoglycans displaying the bottlebrush configuration can be attached to the long hyaluronic acid GAGs via link proteins. These form an even larger complex called aggrecan. The GAGs in this complex then form attachments to the collagen fibers in the matrix. **Aggrecans

The term inflammation refers to a set of specific responses (aka cardinal symptoms) of inflammation:

Redness (Ruber) Swelling (Tumor) Heat (calor) Pain (dolor)

Matrix Metalloproteinases

Since the extracellular matrix is constructed to be a barrier, particularly in connective tissues heavily reinforced by collagen fibers, it becomes necessary to remove or remodel it during some physiological processes; e.g., bone remodeling. This is accomplished using matrix metalloproteinases. These molecules complex with a zinc ion- hence the name. Included among these enzymes are collagenases and gelatinases that dissolve collagen fibers of various types. Note that matrix metalloproteinases are active during the movement of teeth using braces in orthodontistry ***Some micro-organism secrete matrix metalloproteinases in order to invade connective tissue. In addition, cancer cells, which are becoming metastatic, secrete them in order to leave their origin site and enter the blood stream.

Collagen turnover

The collagen in connective tissue is not inert. It is constantly being turned over and renewed. To accomplish this, fibroblasts actually ingest collagen fibrils, use lysosomal degradation to break the fibers back down into their constituent parts, and then make new fibrils from these parts. The periodontal ligament has one of the highest rates of collagen turnover.

Elastic Fibers

The construction of elastic fibers is very different from that of collagen, in line with their different function. Collagen fibers resist being stretched, while elastic fibers give when stretched, but store the energy and return to their original shape, like molecular springs. Elastic fibers have two components: a rather amorphous elastin core region made up of a molecule called elastin, and a surrounding set of microfibrils. These microfibrils are composed of a glycoprotein called fibrillin. When elastic fibers are made, the microfibrils create a hollow tube first, which is then filled with elastin to form the core.

TYPE 1-3 STAINING

The large type I collagen fiber bundles can be visualized easily with H&E stains, where they are eosinophilic. Type II are harder to see because they are found in cartilage, and have the same staining properties as the surrounding cartilage ground substance. Reticular fibers do not stain well with H&E stains. So they are generally demonstrated with special stains. This is demonstrated in your slide sets by pairs of sections, one stained with H&E and the other stained to show the reticular fibers (nest slide).

Inflammation

The transient cells in the connective tissue, along with the mast cells and macrophages, work together to protect the body from invaders. There are a number of ways that they do this. One of them is inflammation. Mast cells have a central role in the process of inflammation. However, realize that the first step in the inflammatory process occurs when a lymphocyte contacts the antigen it is specific for. The lymphocyte then converts into a plasma cell and makes antibodies of the IgE type. These are the ones that bind to the mast cell's IgE receptors. These responses protect the body and bring more of the immune system transient cells into the connective tissue at the site of infection. They are intended to be local. When they become too widespread in the body, the result is anafalaxis, which can soon lead to death as serum drains into the extracellular space and the blood pressure collapses.

Connective Tissue Cells

There are a number of different cell types commonly found in connective tissue proper. These are generally divided into Fixed or Resident cells and Transient cells. Understand that the resident cells spend all or most of their lifespans in the connective tissue, while the transient cells migrate into the connective tissue from the bloodstream for aa short time. Fixed cells Transient cells Authorities differ as to which cells are found in these categories. For example, I have listed macrophages in both categories, as opinions differ on this point. We will leave the discussion of pericytes to the cardiovascular lecture.

Connective Tissue Proper & Embryonic Classes

There are a number of different organizations of the various connective tissue classifications. We will use the following, somewhat simplified approach: Connective Tissue Proper 1. Areolar (Loose) Connective Tissue 2. Dense Irregular Connective Tissue 3. Dense Regular Connective Tissue 4. Adipose Connective Tissue Embryonic Connective Tissue 1. Mesenchyme 2. Mucous Connective Tissue (Wharton's Jelly) Note - that you will not be asked to classify either elastic or reticular connective tissue (which some authorities include as subclasses). Instead, we will be content to just ask you to identify these fiber types.

Mast cell second pathway

There is a second pathway whereby the mast cells act. Crosslinking of the receptor activates a phospholipase pathway which cause membrane bound phospholipids to be converted into arachidonic acid. The arachidonic acid is then converted into leukotrienes and prostaglandins. These also help mediate inflammation and allergic reactions.

Ground Substance: Glycoproteins

These are more accurately termed adhesive glycoproteins. They are large macromolecules that allow cells to stick to the extracellular matrix. To do this, they are characterized by the presence of 3 domains: ---One that allows them to attach to cell surface proteins called integrins. ---A second that allows them to attach to proteoglycans in the ground substance. ---And a third that allows them to attach to fibers in the extracellular matrix, most notably: collagen fibers. Listed below are the some major glycoproteins: examples: fibronectin laminin entactin tenascin chondronectin osteonectin

Fibroblasts / Fibrocytes

These cells produce most of the different types of collagen. They are generally quite flattened and they extend processes along the collagen fibers. As a result, their cytoplasm does not stain well in H&E, and one can only see their flattened nuclei adjacent to collagen bundles. In EM the cytoplasm is pretty non-descript, but the fact this cell is surrounded by banded collagen fibers tips us off as to its identity. The term fibroblast is used to denote cells that are actively making collagen, while fibrocyte refer to cells that are just maintaining collagen in the connective tissue. However, we will not worry about this distinction in the lab and on practical exams: either term will do. *****the most fixed cells are the fibroblasts

Ehlers-Danlos Syndrome

These individuals have a genetic defect that affects lysyl hydroxylase, so their collagen fibrils are not sufficiently cross-linked. This results in collagen fibers that stretch. As a result they have hyper-extendable skin and joints.

Cell Derivation Flowchart

This figure showing cell type derivation includes a lot of cells not covered in this talk and which I will not hold you for at this point. However, it may be useful to you as we go along to organize your understanding of the derivation of various cell types.

Plasma cells

When a lymphocyte meets the specific antigen that it recognizes, it transforms itself in to an antibody making factory. It then pumps out that one specific antibody that recognizes this specific antigen. This functional transformation results in a new morphology, so this active cell is given its own name: Plasma cell. These cells have a bluish tint because they contain lots of rER, they have a large Golgi apparatus that creates a light area (negative Golgi image or hof) in the cytoplasm, and a clock-faced nucleus. Beware of just assuming all cells with clock-faces are plasma cells. Look at the cytoplasm as well.

Elastic fibers features

When elastic fibers are stretched, they uncoil, but are still held together by cross-links. When they are allowed to relax, then they coil up again, returning to their original length. The elastic fibers made by fibroblast are only produced when individuals are in utero or when they are children. So in adults there is a gradual loss of elastic fibers: leading to wrinkles. Disease associated: Marfan syndrome is a genetic defect in the gene that codes for fibrilin leading to improper formation of elastic fibers. Individuals with this defect appear to age very quickly, and are prone to aortic aneurisms.

Identify the structures indicated by the blue, yellow and white pointers

You will need to be able to discriminate elastic from reticular fibers in the special stains, and tell both of them from collagen fibers. Reticular fibers (white arrow) are arranged around the structures they support, this is not true of elastic fibers (blue arrows). Collagen fibers (yellow arrow) are thicker than the other two.

ECM (extracellular matrix)

a complex of macromolecules manufactured by cells and exported into the extracellular space. As you may have gathered, the extracellular space is not just fluid. There are materials dissolved in the fluid. In fact, there are often structural elements within the extracellular fluid. All these elements make up the extracellular matrix. Extracellular matrix is made up of Ground Substance & Fibers. The most important function of extracellular matrix is to provide a structure within the extracellular space. It also: 1.Modifies the morphology & function of cells 2.Influences cell development 3.Regulates cell migration and mitosis 4.Modulates cell survival

Extracellular Fluid

body fluids located outside of cells Living cells cannot exist and function normally outside an aqueous env. The plasma membrane can be seen as the interface btwn the fluid within the cell (intracellular fluid) The water in the extracellular fluid is provided from the serum in the bloodstream, and ultimately comes from the water we consume. Maintaining adequate amounts of water in the body then becomes one of the critical goals of a life form Saliva is a product of the salivary glands emptying in the oral cavity (important for oral health) Water in the saliva is consumed, moved into the blood stream, out of vasculature, and into the ECM; it can then be used to make saliva that is secreted via the ducts of the salivary glands.

White Fat

much more common The adipocytes are entirely filled with a single (hence unilocular) lipid inclusion, as lipid storage is their main function. The cytoplasm is just a thin rim beneath the plasma membrane. The nucleus often sits in a corner of the cell, giving the cell a "signet ring" appearance. White fat can occur as just a cluster of cells, or as sheets in certain areas like the hypodermis. Their distribution is partially defined by sex.

Collagen fibers

provides flexibility and strength Collagen fibers found in the extracellular matrix are mostly made by cells called fibroblasts. However, smooth muscle cells can also make collagen fibers and the cells in bone and cartilage also make collagen.

Brown fat

quite rare in adult humans It is more common in infants and in mammals that hibernate. The adipocytes contain a number of smaller inclusions (hence multilocular). These cells also contain numerous mitochondria, and the function of this tissue is to produce heat.

Reticular Fibers

specialized form of collagen made up of type III Function to form more delicate networks; These networks are specialized to provide support for certain organs, like the liver, spleen and lymph nodes, and certain tissues like adipose tissue and bone marrow. *****RETICULAR FIBERS DO NOT STAIN WELL

Osmotic gradients

the movement of water is crucial to the maintenance of both extracellular and intracellular fluid. It is also necessary for the function of secretory epithelium. the movement of water in and out of the blood stream, in and out of the extracellular fluid, and across the plasma membrane, then in and out of the intracellular fluid is passive ***uses hydrostatic pressure (blood pressure) After that, water generally flows along osmotic gradients: that is it flows from areas where water concentration is higher (solute concentration is lower) to regions where water concentration is lower (and solute concentration is higher). So cells produce water movement by manipulating solute concentration.

Extracellular Matrix - Fibers

three fiber types: 1. collagen fibers 2. reticular fibers 3. elastin fibers As it turns out, reticular fibers are actually a special form of collagen fiber, but from a histology perspective, it is useful to treat reticular fibers as an identifiable form of fiber. In addition there are several different "Types" of collagen fiber that differ in both their organization and the tissues they are found in. There are just two types of elastic fiber recognized histologically.

Uniocular adipocytes appearance

unilocular adipocytes appear empty. The nucleus is generally squashed against the edge of the cell, giving it a signet ring appearance. Adipocytes are most common in the hypodermis, but can appear at a number of other locations. They are well vascularized.

Aquaporins & Pumps

water must either passes around cells, particularly epithelial cells forming borders, like the endothelium lining a capillary, or through cells. To get in or out of a cell, it must pass through the plasma membrane. The lipid bilayer will not allow water to pass, but specialized water channels in the membrane, called aquaporins, allow the passage of water. So the number and type of aquaporin channels a cell possesses are critical to how it regulates water movement. The other critical tool cells use to control water flow is the ability of cells to use ion pumps and channels to move material into the extracellular fluid. By expending energy (ATP) to pump ions or by secreting other materials into the extracellular fluid, cells can manipulate the extracellular environment's osmolarity. In this way, cells can control the flow of water into or out of the extracellular fluid.